Abstract:

The present invention provides an ink composition containing (A) a polymer
compound having (a-1) a photoradical generation site and (a-2) at least
one segregation site selected from a fluoroalkyl group, a siloxane
structure, and a long-chain alkyl group, (B) a radical-polymerizable
compound, and (C) a photoradical generator having a structure different
from that of (A).

Claims:

1. An ink composition comprising:(A) a polymer compound having (a-1) a
photoradical generation site and (a-2) at least one segregation site
selected from a fluoroalkyl group, a siloxane structure, and a long-chain
alkyl group;(B) a radical-polymerizable compound, and(C) a photoradical
generator having a structure different from that of (A).

2. The ink composition of claim 1, wherein the polymer compound (A)
comprises, as a structural unit containing a photoradical generation site
(a-1), at least one structural unit represented by any of formulae
(a-1-1) to (a-1-7), or at least one structural unit represented by
formulae (a-1-8) or (a-1-9): ##STR00059## wherein R10 represents a
hydrogen atom or a methyl group; L represents a single bond or a divalent
linking group; R11, R12, R13 and R14 each
independently represent a linear, branched or cyclic hydrocarbon group
having 1 to 12 carbon atoms which may have a substituent; R11 and
R12, and R13 and R14 may be bound to form a cyclic
structure having a cycle consisting of 8 or less carbon atoms;R15
and R16 each independently represent a linear, branched or cyclic
hydrocarbon group having 1 to 12 carbon atoms which may have a
substituent;R17 represents a hydrogen atom or a linear or branched
alkyl group having 1 to 6 carbon atoms; and R18, R19, and
R20 each independently represent a hydrogen atom or a hydrocarbon
group having 1 to 12 carbon atoms; ##STR00060## wherein R21,
R22, R23, R24 and R25 each independently represent a
hydrogen atom, a linear, branched or cyclic alkyl group having 1 to 8
carbon atoms, a phenyl group, a hydroxyl group, or an alkyl
group-substituted amine group, and two of R21, R22, and
R23 to R25 may be bound to each other to form a ring structure;
R26 and R27 each represent a hydrogen atom, an alkyl group
having 1 to 6 carbon atoms, or a halogen atom;R28, R29,
R30 and R31 each independently represent a hydrogen atom, a
linear or branched alkyl group having 1 to 6 carbon atoms, a halogen
atom, or a hydroxyl group; andR10 and L have the same meanings as
defined in the formula (a-1-1); ##STR00061## wherein R32, R33,
R34 and R35 each independently represent a hydrogen atom, a
hydroxyl group, a halogen atom, or a linear or branched alkyl, alkenyl or
alkynyl group having 1 to 20 carbon atoms, and the alkyl group may, in
its alkyl chain, have non-consecutive oxygen atoms; andL has the same
meaning as defined in the formula (a-1-1).

3. The ink composition of claim 1, wherein a weight-average molecular
weight of (A) the polymer compound is from 5000 to 100,000.

4. The ink composition of any one of claim 1, wherein (A) the polymer
compound further includes (a-3) a radical polymerization site.

6. A method for inkjet recording, the method comprising:(i) jetting the
ink composition of claim 1 onto a recording medium, and(ii) irradiating
the jetted ink composition with an active energy ray, to cure the ink
composition.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims priority under 35 USC 119 from Japanese
Patent Application No. 2009-055460 filed on Mar. 9, 2009, the disclosure
of which is incorporated by reference herein.

BACKGROUND

[0002]1. Field of the Invention

[0003]The present invention relates to an ink composition and an inkjet
recording method and in particular to an ink composition and an inkjet
recording method which are used preferably for inkjet recording by curing
with high sensitivity, by irradiation with active energy rays.

[0004]2. Related Art

[0005]An image recording method of forming an image on a recording medium
such as paper based on an image data signal includes an
electrophotographic method, sublimation and fusion type thermal transfer
methods and an inkjet method. Particularly the inkjet system involves
jetting an ink onto necessary image regions with an inexpensive apparatus
thereby forming the image directly on a recording medium, thus enabling
effective use of ink and reduction in running costs. Moreover, the inkjet
system is excellent as an image recording system because of fewer noises.

[0006]The inkjet system allows printing not only on plain paper but also
on non-water-absorptive recording media such as plastic sheet and metal
plate, but represents important issues for higher speed in printing and
for higher image properties and suffers from drying of droplets after
printing and the time required for curing, thus having a property of
being significantly influenced by productivity of prints and the
sharpness of printed images.

[0007]As one inkjet system, there is a recording system of using a curable
inkjet recording ink by irradiation with radiations. This system involves
irradiation with radiations immediately after ink jetting or within a
given time period after jetting, to cure ink droplets thereby improving
productivity in printing to form sharp images.

[0008]By achieving higher sensitivity in an inkjet recording ink that can
be cured by exposure to radiations such as ultraviolet rays, the ink
produces a large number of benefits such as high curability conferred
toward radiations, improvement in productivity of inkjet recording,
reduction in power consumption, longer lifetime due to decrease in the
load on a radiation generator, and prevention of formation of
low-molecular-weight material volatilizing from insufficient curing. The
achievement in higher sensitivity leads in particular to improvement in
the strength of images formed from the inkjet recording ink.

[0009]Preferable properties of images formed from the ink include
adhesiveness to a substrate and flexibility of images. Particularly when
images are formed on the surface of an uneven substrate or on the surface
of a flexible substrate such as a resin film and further when a print
molding (for example a resin bottle) having a molding formed in a state
provided thereon with a print is formed, the flexibility of images
becomes an important factor and is made hardly compatible with
curability. That is, when the ratio of monofunctional monomers is
increased for improving flexibility, there may be causes wherein
curability is decreased or the image surface tackiness is caused due to
blurring of uncured low-molecular-weight components. Generation of
surface tackiness results in the blocking of prints formed from an ink
composition, deterioration in workability, and deterioration in images
formed, so there has been demand for suppression thereof.

[0010]For improving adhesiveness, flexibility and curability, techniques
of using low-viscosity urethane acrylates in an inkjet ink composition
have been proposed (see, for example, Japanese Patent Application
Laid-Open (JP-A) No. 2002-167537). However, this ink composition hardly
maintains sufficient curability when the content of monofunctional
monomers is increased to form a more flexible ink film.

[0011]Curable ink compositions, particularly radical-polymerizable ink
compositions, are liable to polymerization inhibition with oxygen
adjacent to the surfaces of images formed and are considered subject to
surface tackiness attributable to reduction in the curing property of the
surfaces. Accordingly, techniques wherein surface-oriented functional
groups are introduced into a polymerization initiator and distributed
unevenly on the surface of the polymerization initiator have been
proposed (see, for example, Japanese Patent Application National
Publication (Laid-Open) No. 2004-506639).

[0012]However, the compound having an ability to initiate polymerization
as described herein has failed to sufficiently attain an effect of
suppressing the blocking caused by surface tackiness due to a low glass
transition temperature of the compound.

SUMMARY

[0013]The present invention has been made in view of the above
circumstances and provides an ink composition containing (A) a polymer
compound having (a-1) a photoradical generation site and (a-2) at least
one segregation site selected from a fluoroalkyl group, a siloxane
structure, and a long-chain alkyl group, (B) a radical-polymerizable
compound, and (C) a photoradical generator different from that of (A).

DETAILED DESCRIPTION OF THE INVENTION

[0014]The inventors made extensive study, and as a result, they found that
a polymer compound having, in its molecule, a photoradical generation
site and a surface segregation site can be added to solve the problem,
thereby completing the invention.

[0015]The working effect of the invention is not evident and is estimated
as follows.

[0016]It is estimated in the invention that when (A) the polymer compound
("specific polymer") having (a-1) a photoradical generation site and
(a-2) at least one segregation site selected from a fluoroalkyl group, a
siloxane structure, and a long-chain alkyl group is added to an ink
composition, the polymer compound having an ability to initiate
polymerization is distributed unevenly on the surface of an image formed
from the ink composition, and therefore, the polymerization initiator
becomes unevenly distributed in the outermost region that is usually
hardly curable due to high polymerization inhibition with oxygen at high
density, thereby improving the curability of the outermost surface,
improving abrasion resistance and simultaneously segregating the polymer
compound in the surface, thus improving blocking resistance. Because the
polymer compound is unevenly distributed in the surface, it is considered
that low-molecular components are prevented from leaching out and tack is
not deteriorated.

[0017]In a deep part of the image that is hardly influenced by inhibition
with oxygen, (C) another photoradical generator and (B) a
radical-polymerizable compound, which are contained in the ink
composition of the invention, proceed polymerization and curing
efficiently thereby rapidly forming the ink image prevented from
blocking.

[0018]In a preferable aspect of the invention, the weight-average
molecular weight of (A) the specific polymer is set in the range of 5000
to 100000 and the glass transition temperature (Tg) of the specific
polymer in the range of 20 to 180° C., whereby
low-molecular-weight components can be effectively prevented from
volatilizing and leaching out, and blocking resistance is further
improved. By further introducing polymerizable groups into (A) the
specific polymer, the curability of the surface is improved, and
sensitivity and blocking depression effect are further improved.

[0019]Hereinafter, the invention will be described in detail.

[0020][Ink Composition]

[0021]The ink composition of the invention contains (A) a polymer compound
having (a-1) a photoradical generation site and (a-2) at least one
segregation site selected from a fluoroalkyl group, a siloxane structure,
and a long-chain alkyl group, (B) a radical-polymerizable compound, and
(C) a photoradical generator different from that of (A).

[0022]<(A) Polymer Compound Having (a-1) a Photoradical Generation Site
and (a-2) at Least One Segregation Site Selected from a Fluoroalkyl
Group, a Siloxane Structure, and a Long-Chain Alkyl Group>

[0023](A) The specific polymer used in the invention has, in a molecule,
(a-1) a photoradical generation site and (a-2) at least one segregation
site selected from a fluoroalkyl group, a siloxane structure, and a
long-chain alkyl group.

[0024](a-1) The photoradical generation site is not particularly limited
as long as it has a partial structure for generating radicals by
decomposition with active energy, or by generating hydrogen abstraction
reaction, and the photoradical generation site may be present in the main
chain or side chain of the specific polymer.

[0025]When the photoradical generation site can be introduced via a
covalent bond into the polymer compound, any of known existing
photoradical initiation structures can be used without limitation. In
particular, as a preferable structure, an initiation site in a polymer
type initiator described on pp. 204-225 in Chemistry & Technology of UV &
EB Formulation for Coatings, Ink & Paints can be preferably used.

[0026]As the method of introducing such partial structure, a method of
introducing the partial structure by polymer reaction or a method of
copolymerizing a structural unit having such partial structure thereby
introducing the partial structure can be used, but from the viewpoint of
easiness in regulation of the amount of the structure to be introduced,
the method of copolymerizing the structural unit having a photoradical
generation site is preferable.

[0027]More specifically, the structural units represented by formulae
(a-1-1) to (a-1-9) below are preferably introduced by the method of
copolymerization.

[0028]In the formulae, (a-1) the photoradical generation site is
introduced by inclusion of the structural units represented by the
formulae (a-1-1) to (a-1-7) into a side chain of the specific polymer and
by inclusion of the structural units represented by the formulae (a-1-8)
and (a-1-9) into the main chain of the specific polymer.

[0029]Hereinafter, preferable structural units that constitute the
specific polymer in the invention will be described.

##STR00001##

[0030]In the formulae (a-1-1) to (a-1-4), R10 represents a hydrogen
atom or a methyl group, preferably a methyl group.

[0031]L represents a single bond or a divalent linking group. When L
represents a divalent linking group, the linking group is specifically an
alkylene group having 1 to 20 carbon atoms, an alkenylene group having 2
to 10 carbon atoms, an alkynylene group having 2 to 10 carbon atoms or an
alkylene group having 1 to 20 carbon atoms, where in the alkyl chain, one
or more kinds of non-consecutive oxygen atoms, sulfur atoms, ester bonds,
urethane bonds, urea bonds and thiourea bonds may be included, as well as
phenylene groups which may have a substituent.

[0032]The linking group represented by L may be unsubstituted, or when the
linking group has a substituent, the substituent capable of introduction
into it includes an unsubstituted linear or branched alkyl group having 1
to 12 carbon atoms, a hydroxyl group, an alkoxy group having 1 to 4
carbon atoms, an alkyl group having 1 to 12 carbon atoms which is
substituted with a phenyl group, an alkyl group having 2 to 12 carbon
atoms which has 1 or more non-consecutive oxygen atoms in a chain, a
phenyl group, a carbonyl group, and a sulfonyl group, and L may have one
or more of these groups, and when there are these plural substituents,
they may be the same or different.

[0033]R11, R12, R13 and R14 each independently
represent a linear, branched or cyclic hydrocarbon group having 1 to 12
carbon atoms which may have a substituent and R11 and R12, and
R13 and R14, may be bound to each other to form a cyclic
structure having 8 carbon atoms or less constituting the cycle.

[0034]Particularly, R11 is preferably an alkyl group having 1 to 12
carbon atoms, an unsubstituted phenyl group, or a phenyl group
substituted with an alkyl group having 1 to 4 carbon atoms, and R12
is preferably a hydrogen atom, an unsubstituted alkyl group having 1 to 8
carbon atoms, an alkyl group having 1 to 8 carbon atoms which is
substituted with an OH group or an alkoxy group having 1 to 4 carbon
atoms, an unsubstituted phenyl group, a phenyl group substituted with a
hydroxyl group, an alkyl group having 1 to 4 carbon atoms, and an alkoxy
group having 1 to 4 carbon atoms; an alkylene group having 1 to 12 carbon
atoms which may contain a heteroatom, an ethyleneoxide group, a
propyleneoxide group, an alkylester group, a phenylene group, or a phenyl
alkyl group. R11 may further have a substituent introduced into it,
and the substituent capable of introduction into it includes a hydroxyl
group, a halogen atom, a thioether group and a phenyl group.

[0035]R15 and R16 each independently represent a linear,
branched or cyclic hydrocarbon group having 1 to 12 carbon atoms which
may have a substituent. R15 and R16, together with a nitrogen
atom bound thereto, are bound to a carbon atom constituting R15 and
R16-- or may together with a carbon atom form a 5-, 6- or
7-memberred ring including --O-- or an amino group.

[0036]Each of R15 and R16 is preferably a hydrocarbon group
having 1 to 12 carbon atoms, an unsubstituted phenyl group, a phenyl
group substituted with one kind or more substituent selected from an
alkyl group having 1 to 4 carbon atoms, and an alkoxy group having 1 to 4
carton atoms.

[0037]The substituents that can be introduced into R15 and R16
include those substituents capable of introduction into the linking group
L.

[0038]R17 represents a hydrogen atom or a linear or branched alkyl
group having 1 to 6 carbon atoms, and R18, R19, and R20
each independently represent a hydrogen atom or a hydrocarbon group
having 1 to 12 carbon atoms.

##STR00002##

[0039]In the formula (a-1-5), R21, R22, R23, R24 and
R25 each independently represent a hydrogen atom, a linear, branched
or cyclic alkyl group having 1 to 8 carbon atoms which may have a
substituent, a phenyl group which may have a substituent, a hydroxyl
group, an alkyl group-substituted amine group, or a cyano group, and two
of R21, R22, and may be bound to each other to form a ring
structure.

[0040]Specifically, with respect to the phenyl group to which groups
R23 to R25 are to be bound, it is preferably a structure which
is unsubstituted or a mono-substituent at position 4 relative to
carbonyl, more preferably unsubstituted or a mono-substituent at position
4 relative to carbonyl with a phenyl group, a phenoxy group, a cyano
group, a hydroxyl group, a methoxy group, a methyl group or a
dimethylamino group.

[0041]In the formula (a-1-6), R26 and R27 each represent a
hydrogen atom, an alkyl group having 1 to 6 carbon atoms, or a halogen
atom.

[0042]Specifically, R26 and R27 each represent a methyl group,
an ethyl group, a chlorine atom or a bromine atom, preferably a methyl
group.

[0043]In the formula (a-1-7), R28, R29, R39 and R31
each independently represent a linear or branched alkyl group having 1 to
6 carbon atoms, a halogen atom, or a hydroxyl group.

[0044]More specific examples of R28, R29, R30, and R31
include a methyl group, an ethyl group, an isopropyl group, a
2-ethylhexyl group, a chlorine atom, a bromine atom and a fluorine atom,
preferably a methyl group, an isopropyl group and a chlorine atom.

[0045]In the formulae (a-1-5) to (a-1-7), R10 and L have the same
meanings as defined in the formula (a-1-1), and preferable examples
thereof are also the same as defined therein.

[0046]Hereinafter, structural units for introduction of (a-1) the
photoradical generation site into the side chain will be illustrated, but
the invention is not limited thereto.

##STR00003## ##STR00004## ##STR00005## ##STR00006## ##STR00007##

[0047]Hereinafter, the partial structure for introducing the photoradical
generation site by polycondensation will be illustrated.

##STR00008##

[0048]In the formulae (a-1-8) to (a-1-9), R32, R33, R34 and
R35 each independently represent a hydrogen atom, a hydroxyl group,
a halogen atom, or a linear or branched alkyl, alkenyl or alkynyl group
having 1 to 20 carbon atoms, and the alkyl group may, in its alkyl chain,
have non-consecutive oxygen atoms.

[0049]Preferable among them are a methyl group, an ethyl group, an
isopropyl group, an isobutyl group, a 2-ethylhexyl group, a methoxy
group, an ethoxy group, a chlorine atom, a bromine atom, an acryloyl
group, and a methacryloyl group.

[0050]L is the same as in the formula (a-1-1), and preferable examples
thereof are also the same as defined therein.

[0051]Hereinafter, specific examples of the structure unit for introducing
the photoradical generation site by polycondensation are shown below, but
the invention is not limited thereto.

##STR00009##

[0052](A) The specific polymer in the invention may include only one kind
of structure including (a-1) the photoradical generation site or two
kinds or more structures thereof.

[0053]The content of (a-1) the photoradical generation site in (A) the
specific polymer in the invention is preferably such that the structural
units are contained in the range of 10 to 99% by weight, more preferably
50 to 99% by weight, from the viewpoint of blocking suppression and
dissolution.

[0054]<(a-2) At Least One Segregation Site Selected from a Fluoroalkyl
Group, a Siloxane Structure, and a Long-Chain Alkyl Group>

[0055](A) The specific polymer in the invention has (a-2) at least one
segregation site selected from a fluoroalkyl group, a siloxane structure,
and a long-chain alkyl group (hereinafter referred to merely as
segregation site).

[0056]Hereinafter, these partial structures will be described.

[0057][(a-2-1) Fluoroalkyl Group]

[0058]The fluoroalkyl group in the specific polymer in the invention
refers to a structure including an alkyl or alkylene group substituted
with at least one fluorine atom. The fluoroalkyl group herein includes a
fluoroalkyl group wherein at least one hydrogen atom in the alkyl or
alkylene group has been replaced by a fluorine atom, and the fluoroalkyl
group is preferably a perfluoroalkyl or perfluoroalkylene group having
every hydrogen atom in the alkyl or alkylene group has been replaced by
fluorine atoms, among them, a perfluoroalkyl group having every hydrogen
atom in the alkyl group has been replaced is more preferable.

[0059]The alkyl group is one having preferably 3 to 12 carbon atoms, more
preferably 4 to 10 carbon atoms, still more preferably 6 to 8 carbon
atoms.

[0060]The alkylene group is one having preferably 2 to 12 carbon atoms,
more preferably 4 to 10 carbon atoms, still more preferably 6 to 8 carbon
atoms.

[0061]Specific aspects of the fluorine-substituted hydrocarbon groups in
the invention will be described.

[0062]Preferable fluorine-substituted hydrocarbon groups possessed by the
specific polymer include those represented by (a2-1) or (a2-2) shown
below.

[0063](a2-1) Substituent (hereinafter referred to sometimes as
"fluoroaliphatic group") derived from a fluoroaliphatic compound produced
by a telomerization or oligomerization method.

[0064](a2-2) Substituent represented by the following (formula I):

##STR00010##

[0065]In the above (formula I), R2 and R3 each independently
represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, X
represents a covalent bond or a divalent linking group (organic group), m
represents an integer of 0 or more, and n represents an integer of 1 or
more.

[0066]When m is 2 or more, functional groups on mutually adjacent carbons
(that is, R2 and R3 groups on mutually adjacent carbons) may be
bound to each other to form an aliphatic ring.

[0067]The substituents represented by (formula I) are linked via the
portion * to the polymer main chain.

[0068](a2-1) Substituent Derived from a Fluoroaliphatic Compound Produced
by a Telomerization or Oligomerization Method

[0069]The fluorine-substituted alkyl group in the invention is preferably
a substituent (fluoroaliphatic group) derived from a fluoroaliphatic
compound produced by a telomerization method (also called a telomere
method) or an oligomerization method (also called an oligomer method).

[0070]The method for production of such fluoroaliphatic group is described
in, for example, "Synthesis and Functions of Fluorine Compounds", pp.
117-118, supervised by Nobuo Ishikawa and published by CMC, 1987, and
"Chemistry of Organic Fluorine Compounds II", pp. 747-752, Monograph 187,
Ed by Milos Hudlicky and Attila E. Ravlath, American Chemical Society
1995.

[0071]The telomerization method is a method wherein a telomere is
synthesized by radical polymerization of a fluorine-containing vinyl
compound such as tetrafluoroethylene, by using, as a telogen, an alkyl
halide (for example an iodide) having a large chain transfer constant.

[0072]In the invention, the fluoroaliphatic compound synthesized by the
telomere method is preferably a fluoroaliphatic compound represented by
the formula [TM-1] below.

[0073]When such fluoroaliphatic compound is used as it is or after being
converted into the desired monomer structure, the fluorine-substituted
hydrocarbon groups can be introduced into the specific polymer in the
invention.

##STR00011##

[0074]In the formula [TM-1], T represents one kind of group selected from
the following (group T), Z is one kind of group selected from the
following (group Z), and n represents an integer of 0 to 20.

[0075]The fluoroaliphatic compound represented by the formula [TM-1], when
having a polymerizable group such as a double bond in Z, may be used as a
copolymer component in synthesizing the specific polymer in the
invention.

##STR00012##

[0076]When the group represented by Z in the formula [TM-1] is one kind of
group selected from the following (group Z'), the group comes to have a
structure having an acryloyl or methacryloyl group in a molecular end.
Accordingly, this is particularly preferable because the specific polymer
in the invention can be obtained easily by vinyl polymerization from the
fluoroaliphatic compound represented by the formula [TM-1].

##STR00013##

[0077]Specific examples of compounds produced by the telomere method
(commercial products based on fluoroaliphatic compounds represented by
the formula [TM-1]), used preferably in synthesizing the specific polymer
in the invention, include for example fluorine-based chemical products
available from Daikin Chemicals Sales Co., LTD. and CHEMINOX FA, FA-M,
FAAC, FAAC-M, FAMAC and FAMAC-M manufactured by Nippon Mektron, Ltd.

[0078]The fluoroaliphatic compound produced by the telomere method can be
used in easily synthesizing a polymer having a fluoroaliphatic group in a
side chain, such as the specific polymer in the invention, by a method
known to those skilled in the art.

[0079]The substituent derived from the fluoroaliphatic compound produced
by the oligomerization method (oligomer method) is also preferable in the
invention.

[0080]The oligomerization method is a method wherein tetrafluoroethylene
is subjected to cationic polymerization with potassium fluoride or cesium
fluoride as a catalyst, in a polar solvent such as diglyme, thereby
producing the corresponding oligomer. As a specific example, Synthesis
Example 3 below is shown.

[0081]The fluoroaliphatic compound obtained by the oligomer method,
similar to the compound obtained by the telomere method, is subjected to
cationic polymerization to give an oligomer having polymerizable groups
(unsaturated bonds). which are then utilized if necessary with suitable
chemical modifications, whereby a polymer having, in a side chain, a
substituent (fluorine-containing hydrocarbon group) derived from the
fluoroaliphatic compound can be systhesized.

SYNTHESIS EXAMPLE 3

##STR00014##

[0083](a2-2) Substituent Represented by (Formula I)

[0084]From the viewpoint of uneven distribution in the ink surface, the
specific polymer in the invention preferably has substituents represented
by the following (formula I):

##STR00015##

[0085]In the above (formula I), R2 and R3 each independently
represent a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, *
represents a linking site to the polymer chain, X represents a covalent
bond or a divalent linking group, m represents an integer of 0 or more,
and n represents an integer of 1 or more.

[0086]When m is 2 or more, functional groups on mutually adjacent carbons
(that is, R2 and R3 groups on mutually adjacent carbons) may be
bound to each other to form an aliphatic ring.

[0087]In the substituent represented by the above (formula I), "n" in
(formula I) is preferably 1 to 10, more preferably 1 to 4, even more
preferably 2 or 3.

[0088]That is, the specific polymer in the invention is preferable because
the structure of the side-chain portion bound to the polymer main chain
is a structure represented by the following (formula IB) wherein n is
particularly 2, 3 or 4 thereby exhibiting extremely performance.

##STR00016##

[0089]In the above (formula IB), R2, R3, X, m and n each have
the same meanings as defined in R2, R3, X, m and n in (formula
I), respectively.

[0090]The alkyl group having 1 to 4 carbon atoms represented by each of
R2 and R3 in (formula I) and (formula IB) includes a methyl
group, an ethyl group, a propyl group, an isopropyl group, an n-butyl
group, an isobutyl group, and a tert-butyl group, and is preferably a
hydrogen atom or a methyl group, more preferably a hydrogen atom.

[0091]In (formula I) and (formula IB), it is meant that when X is a
covalent bond, the polymer main chain, and the carbon atom through which
R2 and R3 are bound, are directly bound to each other.

[0092]When X is a divalent linking group, the linking group includes
--O--, --S--, --N(R4)--, --CO--. Among them, --O-- is more
preferable.

[0093]R4 represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms. The alkyl group includes a methyl group, an ethyl group, a
propyl group, an isopropyl group, an n-butyl group, an isobutyl group and
a tert-butyl group, among which a hydrogen atom or a methyl group is
preferable.

[0094]In (formula I) and (formula IB), m represents an integer of 0 or
more, preferably an integer of 2 to 8, particularly preferably 2. When m
is 2 or more, functional groups on mutually adjacent carbons (that is,
R2 and R3 groups on mutually adjacent carbons) may be bound to
each other to form an aliphatic ring.

[0095]In (formula I) and (formula IB), n represents an integer of 1 or
more, preferably an integer of 1 to 10, more preferably 1 to 4, even more
preferably 2 or 3.

[0096]In (formula I), * represents a linking site to the polymer main
chain, and there are the following examples in the specific mode of the
polymer main chain.

[0098]1) Specific polymer having a fluorine-substituted hydrocarbon group
in the invention can be obtained easily by methods known to those skilled
in the art, such as condensation polymerization, addition polymerization
or ring-opening polymerization, by suitably selecting (A) the monomer
having a fluoroaliphatic group and (B) the monomer having a substituent
represented by the above (formula I) (that is, the monomer having a
fluorine-substituted hydrocarbon group). If necessary, these monomers can
be mixed to produce the polymer.

[0099](Monomer Having a Fluorine-Substituted Hydrocarbon Group)

[0100]In the invention the specific polymer is obtained preferably by
using the monomer having a fluorine-substituted hydrocarbon group
(hereinafter referred to as the fluorine-substituted hydrocarbon
group-containing monomer).

[0102]In (formula II), R1 represents a hydrogen atom, a halogen atom,
a methyl group which may have a substituent or an ethyl group which may
have a substituent. R2, R3, X, m and n have the same meanings
as defined in R2, R3, X, m and n in (formula I), respectively,
and preferable examples thereof are also the same as defied therein.

[0103]The halogen atom represented by R1 in (formula II) includes,
for example, a fluorine atom, a chlorine atom and a bromine atom.

[0104]Hereinafter, specific examples of the monomers represented by the
above (formula II) used in the invention will be illustrated.

[0105]Specific examples wherein n=4

##STR00018## ##STR00019##

[0106]Specific examples wherein n=3

##STR00020## ##STR00021##

[0107]Specific examples wherein n=1

##STR00022## ##STR00023##

[0108]Specific examples wherein n=2

##STR00024## ##STR00025##

[0109]The monomers used in synthesis of the specific polymer in the
invention are those monomers of the above (formula II) wherein "n" is
preferably 1 to 10, more preferably 1 to 4, still more preferably 2 or 3,
among the monomers represented by the above (formula II).

[0110]As a diol used in forming the urethane structure described above, a
diol having a fluoroalkyl group can be used to introduce a fluoroalkyl
group into (A) the specific polymer. The diol having a fluoroalkyl group
can be obtained by treating a fluoroalkyl group having an epoxy group at
the terminal thereof with an acid catalyst according to a method
described in JP-A No. 2005-126357. By this method, for example,
fluoroalkyl 1,2-diol can be obtained with high yield.

[0111]For introduction of a fluoroalkyl group into (A) the specific
polymer, a compound including a fluoroalkyl group having an epoxy group
may be used. The fluoroalkyl compound having an epoxy group is available
as a commercial product, and examples include E-1430, E-1630, E-1830,
E-2030, E-5244, E-5444, E-5644, E-5844, and E-7432 manufactured by Daikin
Industies, Ltd.

[0112][(a-2-2) Siloxane Structure]

[0113]The siloxane structure included in (A) the specific polymer in the
invention is not particularly limited as long as it has, as a partial
structure, a siloxane skeleton represented by "--Si--O--Si--".

[0114]In the invention, the specific polymer having a siloxane structure
is preferably a compound constituted to include a structural unit having
a siloxane structure in a side chain, from the viewpoint of increasing
the jetting stability of an ink composition and of increasing surface
segmentation upon formation of the ink composition into a coating film.

[0115]The siloxane compound useful in introducing the siloxane structure
intramolecularly into (A) the specific polymer is available as a
commercial product and includes, for example, one-terminal-reactive
silicones such as X-22-173DX and X-22-173BX manufactured by Shin-Etsu
Chemical Co., Ltd.

[0116]The siloxane skeleton can also be synthesized by reacting a siloxane
having a reactive terminal, with a compound having a cationic
polymerizable group. The siloxane skeleton may be synthesized for example
from a compound having a one-terminal hydroxyl group (for example,
Silaplane series FM-0411, FM-0421 and FM-0425 manufactured by Chisso
Corp.) and epichlorohydrin or by synthesis in accordance with a method
described in JP-A No. 11-80315.

[0117]The siloxane skeleton in the invention includes, but is not limited
to, the following structures.

##STR00026##

[0118][(a-2-3) Long-Chain Alkyl Group]

[0119]<Alkyl Group Having 6 or More Carbon Atoms>

[0120]The alkyl group having segregation property, which constitutes the
segregation site in the invention, is not particularly limited as long as
it is an alkyl group having 6 or more carbon atoms, and the alkyl group
may be linear, branched or cyclic but is preferably linear. The number of
carbon atoms in the group is 6 to 40, more preferably 6 to 18, even more
preferably 6 to 12.

[0121]The alkyl group having 6 or more carbon atoms, which is present in
the side chain in (A) the specific polymer contained in the ink
composition of the invention, is a substituent represented by
--CnH2n+1 in formula (III) below, and preferably includes the
structural unit represented by the formula (III), thereby being
introduced into the polymer.

##STR00027##

[0122]In the formula (III), n represents an integer of 6 to 40, preferably
6 to 18, even more preferably 6 to 12, from the viewpoint of segregation
property.

[0123]Y represents a polymer main chain, and --CnH2n+1 (an alkyl
group having 6 or more carbon atoms) is bound directly or via a binding
group to this main chain.

[0124]W represents a single bond or a linking group, and when W represents
a single bond, the long-chain alkyl group is bound directly to the
polymer main chain. Z1 represents a hydrogen atom or a monovalent
substituent.

[0125]The 6 or more alkyl groups in the formula (III) may be present
plurally in the structure unit, and in this case, use can be made to the
aspect wherein an alkyl group having 6 or more carbon atoms is bound via
the linking group W to the position Z1 or to the aspect wherein the
linking group W has a branched structure or a cyclic structure, and any
of carbon atoms constituting W may be connected via its end to another
alkyl group having 6 or more carbon atoms.

[0127]R and R' each represent a hydrogen atom, a liner or branched alkyl
group, a linear or cyclic alkyl group, a linear or branched alkenyl
group, a linear or cyclic alkenyl group, a linear or branched alkynyl
group, or a linear or cyclic alkynyl group, and Ar and Ar' each represent
an aryl group.

[0129]In the invention, the linking group represented by W may be a
combination of two or more linking groups mentioned herein.

[0130]Hereinafter, the divalent substituent represented by W includes
particularly preferable examples form the viewpoint of segregation on ink
surface, but the invention is not particularly limited thereto.

##STR00028##

[0131]Z1 includes not only the aspect wherein a long-chain alkyl
group is bound via the linking group W, but also groups shown below. When
m is 6 or more to 20 or less, Z1 can have a long-chain alkyl group
in such an aspect.

##STR00029##

[0132]Hereinafter, specific examples of the structural unit having a
long-chain alkyl group in the invention are shown below, but the
invention is not limited thereto.

[0137]The content of the partial structure selected from the group
consisting of (a-2-1) fluoroalkyl group, (a-2-2) siloxane skeleton and
(a-2-3) long-chain alkyl group, in (A) the specific polymer in the
invention, is preferably 0.3 to 40% by weight, more preferably 0.5 to 30%
by weight, even more preferably 1 to 20% by weight, based on the weight
of the specific polymer.

[0138]With this ratio, the specific polymer can be effectively
surface-segregated in the ink composition.

[0139]<(a-3) Radical Polymerization Group>

[0140]The specific polymer in the invention preferably has (3) the
radical-polymerizable group in a side chain.

[0142]The radical-polymerizable group includes polymerizable groups having
a radical-polymerizable ethylenically unsaturated bond.

[0143]Examples of the polymerizable group having a radical-polymerizable
ethylenically unsaturated bond include unsaturated carbonate groups such
as an acrylate group, a methacrylate group, an itaconate group, a
crotonate group, an isocrotonate group and a maleate group, as well as
radical-polymerizable groups such as a styrene group. Among them, a
methacrylate group and an acrylate group are preferable.

[0144]The content of the radical-polymerizable group in the specific
polymer is preferably 0 to 80 mol %, more preferably 10 to 60 mol %, more
preferably 30 to 60 mol %.

[0145]The method of introducing the radical-polymerizable group into the
specific polymer includes a method wherein a monomer having a
radical-polymerizable group double bond sealed by reaction with a
protective group is used and this monomer is copolymerized to eliminate
the protective group thereby forming a radical-polymerizable group
(double bond) or a method wherein a low-molecular-weight compound having
a radical-polymerizable group is introduced by polymerization reaction
into the specific polymer.

[0146]Hereinafter, specific examples of (a-3) the radical-polymerizable
group will be described. However, the invention will not be limited to
these examples.

##STR00033## ##STR00034##

[0147]The specific polymer in the invention essentially has (a-1)
photoradical polymerization site and (a-2) surface segregation site
selected from the group consisting of (a-2-1) fluoroalkyl group, (a-2-2)
siloxane skeleton and (a-2-3) long-chain alkyl group and further
preferably includes (a-3) radical-polymerizable group, and may further
include copolymerizable components (other copolymerizable components)
having other structures. The other copolymerizable compounds are
preferably used in the specific polymer, from the viewpoint of
improvement in insolubility in the ink composition and of improvement in
blocking property by regulation of polymer Tg.

[0148]The main structure of the specific polymer contained in the ink
composition of the invention is not particularly limited, and may be a
methacrylic resin or an acrylic resin and may be the main chain structure
composed of a urethane bond or a urea bond.

[0149](Other Copolymerizable Components)

[0150]The other copolymerizable components that constitute (A) the
specific polymer in the invention include not only general monomers for
solubility, Tg, and regulation, but also a monomer having an amine group
as a intramolecular hydrogen donor, a monomer having a Si--H group and a
monomer having a radical-polymerizable precursor, and is used preferably
in combination with monomers capable of formation, by polymerization
reaction after copolymerization, into a polymer having
radical-polymerizable groups.

[0151]The other structural units include, for example, the following
compounds.

[0153]By adding these copolymerizable components, the Tg of the whole
polymer is preferably made room temperature or more.

[0154]The content of other copolymerizable components in the specific
polymer is preferably in the range of 0 to 50% by weight, more preferably
0 to 30% by weight, most preferably 0 to 20% by weight.

[0155]Hereinafter, specific examples [specific polymers (a-1) to (a-23)]
of (A) the specific polymer of the invention will be illustrated by
clearly specifying their structural units, polymerization molar ratios
and weight average molecular weights (Mw), but the invention is not
limited thereto.

[0156]The molecular weight of (A) the specific polymer, in terms of
weight-average molecular weight determined by GPC, is preferably 5000 to
100000, more preferably 8000 to 100000, most preferably 10000 to 100000.

[0157]When the specific polymer itself has adhesiveness upon aggregation
thereon, its inhibitory effect on blocking will not brought about.
Accordingly, the polymer should have a molecular weight enough to exhibit
a physical property for showing a certain glass transition temperature,
specifically a Tg of 20° C. or more. When the weight-average
molecular weight is smaller than the above range, low-molecular oligomer
components having a molecular weight of 1000 or less is increased in the
molecular-weight distribution, and thus the inhibitory effect on blocking
may not be sufficiently brought about.

[0158]That is, (A) the specific polymer selected in the invention is
preferably one having a glass transition temperature (Tg) of 20 or more
to 180° C. or less, more preferably 20 or more to 100° C.
or less. The Tg used in the invention is a value measured at an
increasing temperature rate of 10° C./min with a differential
scanning calorimeter (DSC).

[0159]The Tg of (A) the specific polymer can be regulated not only by
regulating the molecular weight, but also for example by introducing
structural units such as methyl methacrylate, isobornyl methacrylate,
FA-513A and bisphenol A and then regulating the amounts of the structural
units introduced.

[0160]The content of the specific polymer on a weight basis is preferably
0.2 to 10% by weight, more preferably 0.2 to 8% by weight, still more
preferably 0.2 to 5% by weight, relative to the total solids of the ink
composition in the invention. When the content is in this range, the
inkjet ink can improve surface hardness and blocking suppression without
exerting adverse influence on the necessary physical properties.

[0163](B) The radical-polymerizable compound is a compound having a
radical-polymerizable ethylenically unsaturated bond, and may be any
compound having at least one radical-polymerizable ethylenically
unsaturated bond in a molecule, and examples thereof include those having
a chemical configuration such as a monomer, an oligomer, or a polymer.
One type of radical-polymerizable compound may be used, or two or more
types thereof may be used at an arbitrary ratio in order to improve an
intended property. It is preferable to use two or more types of compounds
in combination, from the viewpoint of regulating performances such as
reactivity and physical properties.

[0166]Furthermore, as the radical-polymerizable compounds, photo-curable
polymerization materials that are used in photo-polymerizable
compositions described in, for instance, JP-A No. 7-159983, JP-B No.
7-31399, JP-A Nos. 8-224982, 10-863 and 9-134011 are known and these can
be applied as well in the ink composition of the invention.

[0168]Of the vinyl ether compounds, the di- or tri-vinyl ether compounds
are preferred and divinyl ether compounds are particularly preferred from
the viewpoint of curability, adhesiveness and surface hardness. The vinyl
ether compounds can be used singularly or in a combination of two or more
appropriate kinds.

[0169]In the total solid content of the ink composition of the invention,
the content of (B) the radical-polymerizable compound is preferably 55 to
90% by weight, more preferably 60 to 85% by weight, based on the total
amount of the ink composition. Given this ratio given, coating films
excellent in curability and color reproduction can be obtained.

[0170]For improving the flexibility of the coating film, the content of
monofunctional monomers in the radical-polymerizable compound is
preferably 60 to 100% by weight, more preferably 80 to 100% by weight,
even more preferably 90 to 100% by weight.

[0171][(C) Photoradical Generator Different from (A) the Specific Polymer]

[0172]The ink composition of the invention contains (C) photoradical
generator different from (A) the specific polymer. As (C) the
photoradical generator different from (A) the specific polymer, a known
photopolymerization initiator can be appropriately selected in accordance
with the type of the simultaneously used components that are (A) the
specific polymer and the polymerizable compound (B), as well as the
intended object of the ink composition.

[0173](C) The photopolymerization initiator used in the ink composition of
the invention is a compound that absorbs an external energy (light) to
generate a radical as a photopolymerization initiator. The light can be
exemplified by active radiations, that is, γ-rays, β-rays,
electron beam, UV-rays, visible rays and IR-rays.

[0175]The radical polymerization initiator may be a single compound or a
combination of compounds selected from the above-mentioned (a) to (m).
The radical polymerization initiators in the invention may be used
singularly or in a combination of two or more kinds.

[0178](C) The photoradical generators can be used alone or as a mixture of
two or more thereof.

[0179](C) The content of the photoradical initiator in the ink composition
is preferably in the range of 0.1 to 20% by weight, more preferably 0.5
to 10% by weight, even more preferably 1 to 7% by weight, in terms of
solids content based on the ink composition.

[0180]<Other Additives>

[0181]The inkjet recording ink composition of the invention may contain
other components simultaneously for the purpose of improvement in
physical properties in addition to the essential components as long as
the effect of the invention is not impaired.

[0182]Hereinafter, these arbitrary components will be described.

[0183]The ink composition of the invention may further contain, as
co-sensitizers, known components having actions such as further
improvement in sensitivity or suppression of the polymerization
inhibition with oxygen.

[0184]Examples of the co-sensitizer include amines such as those described
in "Journal of Polymer Society" written by M. R, Sander et al., vol. 10,
p. 3173 (1972), JP-B No. 44-20189, JP-A Nos. 51-82102, 52-134692,
59-138205, 60-84305, 62-18537, and 64-33104 and Research Disclosure
33825. Specific examples thereof include triethanolamine, ethyl
p-dimethylaminobenzoate, p-formyldimethylaniline, and
p-methylthiodimethylaniline.

[0185]Other examples of the co-sensitizer includes thiols and sulfides,
for example thiol compounds described in JP-A No. 53-702, JP-B No.
55-500806, and JP-A No. 5-142772, and disulfide compounds described in
JP-A No. 56-75643. Specific examples thereof include
2-mercaptobenzothiazole, 2-mercaptobenzoxazole, 2-mercaptobenzimidazole,
2-mercapto-4(3H)-quinazoline, and β-mercaptonaphthalene.

[0187]The amount of the co-sensitizer added is suitably selected depending
on the intended object and is generally 0.01 to 10% by weight based on
the total amount (total mass) of the ink composition.

[0188]<Surfactant>

[0189]The ink composition of the invention preferably contains known
surfactants. The known surfactants include those described in JP-A Nos.
62-173463 and 62-183457. In place of the known surfactant, an
organofluoro compound may be used. The organofluoro compound is
preferably hydrophobic. Examples of the organofluoro compound include a
fluorine-containing surfactant, an oily fluorine-base compound (for
example, fluorine oil) and a solid fluorine compound resin (for example,
ethylene tetrafluoride resin). The organofluoro compound is described in
JP-B 57-9053 (columns 8 to 17) and JP-A 62-135826.

[0190](Colorant)

[0191]The ink composition of the invention can contain a colorant as
necessary. By adding a colorant to the ink composition, the ink
composition can form a visible image (colored image).

[0192]The colorant that can be used in the ink composition of the
invention is not particularly limited, and can appropriately select and
use a wide variety of known colorants (pigments, dyes) depending on
intended purposes. For example when images excellent in weatherability
are to be formed, pigments are preferable. As dyes, both water-soluble
dyes and oil-soluble dyes may be used, among which the oil-soluble dyes
are preferable.

[0193](1. Pigment)

[0194]First, a pigment used preferably as the colorant in the ink
composition of the invention will be described in detail. When the
pigment is used as a colorant, a colored image formed with the ink
composition is made excellent in light resistance.

[0195]The pigment is not particularly limited, and all generally
commercial organic or inorganic pigments, pigments dispersed in an
insoluble resin as a dispersant, and pigments having a surface grafted
with a resin may be used. In addition, resin particles dyed with a dye
may also be used.

[0197]Specific examples of the inorganic or organic pigments that can be
used in the invention include compounds shown in paragraph numbers [0126]
to [0131] in JP-A No. 2008-13646, and these can be used in the invention
as well.

[0198]For dispersion of the pigment, for example, a dispersing machine
such as a ball mill, a sand mill, an attritor, a roll mill, a jet mill, a
homogenizer, a paint shaker, a kneader, an agitator, a henschel mixer, a
colloidal mill, an ultrasonic homogenizer, a pearl mill, or a wet type
jet mill may be used.

[0199]To carry out dispersion of the pigment, a dispersant may be added.
Examples of the dispersant include hydroxyl group-containing carboxylic
acid esters, salts of a long-chain polyaminoamide and a high molecular
weight acid ester, high molecular weight polycarboxylic acid salts, high
molecular weight unsaturated acid esters, high molecular weight
copolymers, modified polyacrylates, aliphatic polycarboxylic acids,
naphthalenesulfonic acid formaldehyde condensates, polyoxyethylene
alkylphosphate esters, and pigment derivatives. It is also preferable to
use a commercial polymeric dispersant such as SOLSPERSE series
manufactured by Lubrizol Corporation.

[0200]Furthermore, as a dispersion adjuvant, a synergist, depending on the
various types of pigment can be used. The dispersant and dispersion
adjuvant are preferably added in an amount of 1 to 50 parts by weight
relative to 100 parts by weight of the pigment.

[0201]In the ink composition, a solvent may be added as a dispersing
medium for various components such as the pigment, or the polymerizable
compound that is a solvent-free low-molecular-weight component may be
added as a dispersing medium. The ink composition of the invention is a
radiation curing type ink, and the ink is cured after application onto a
recording medium, it is preferable not to use a solvent. This is because,
if a solvent remains in the cured ink image, the solvent resistance is
degraded and the VOC (Volatile Organic Compound) problem of the residual
solvent occurs. From this viewpoint, the polymerizable compound is
preferably used as the dispersion medium, and selection of a cation
polymerizable monomer lowest in viscosity among them is preferable for
improvement in dispersibility and handleability of the ink composition.

[0202]The volume-average particle size of the pigment particles in the ink
composition is preferably in the range of 0.02 to 0.60 μm, more
preferably 0.02 to 0.10 μm. The maximum particle size is preferably 3
μm or less, more preferably 1 μm or less, for the range of which
the pigment, dispersant and dispersion medium are selected and dispersion
conditions and filtering conditions are established. When the particle
size is thus managed, a head nozzle can be inhibited from clogging, and
the storage stability of ink, the transparency of ink and the curing
sensitivity of ink can be maintained.

[0203](2. Dye)

[0204]Then, the dye used preferably as the colorant in the invention will
be described.

[0205]Conventionally known compounds (dyes) can be suitably selected and
used as the dye. Specifically, compounds described in paragraph numbers
[0023] to [0089] in JP-A No. 2002-114930 and in paragraph numbers [0136]
to [0140] in JP-A No. 2008-13646 can be mentioned and used in the
invention.

[0206]These colorant are added in an amount of 0.05 to 20% by weight, more
preferably 0.2 to 10% by weight, based on the total amount (total mass)
of the ink composition. When an oil-soluble dye is used as the colorant,
the amount of the oil-soluble dye is particularly preferably 0.2 to 6% by
weight based on the total mass (including the solvent) of the ink
composition.

[0207](Additives)

[0208]The ink composition of the invention can contain various additives
together as necessary in addition to the essential components. These
arbitrary components will be described below.

[0209]--UV Absorber--

[0210]The ink composition of the invention may contain a UV absorber from
the viewpoint of improving the weather resistance of an image to be
obtained and of preventing discoloration.

[0212]The amount thereof added is appropriately selected according to the
intended application and is generally on the order of 0.01 to 10% by
weight based on the total amount (total mass) of the ink composition.

[0215]The amount of the antioxidant added is appropriately selected
suitably depending on the object, but is generally about 0.01 to 10% by
weight based on the total amount (total mass) of the ink composition.

[0216]--Antifading Agent--

[0217]The ink composition of the invention may employ various organic and
metal complex antifading agents. The organic antifading agents include
hydroquinones, alkoxyphenols, dialkoxyphenols, phenols, anilines, amines,
indanes, chromans, alkoxyanilines, and heterocycles. The metal complex
antifading agents include nickel complexes and zinc complexes. More
specifically, there can be used compounds described in patents cited in
Research Disclosure, No. 17643, Items VII-I to J, Research Disclosure,
No. 15162, Research Disclosure, No. 18716, page 650, left-hand column,
Research Disclosure, No. 36544, page 527, Research Disclosure, No.
307105, page 872, and Research Disclosure, No. 15162, and compounds
contained in formulae and compound examples of typical compounds
described in JP-A No. 62-215272, pages 127 to 137.

[0218]The amount thereof added is appropriately selected according to the
intended application, but is preferably on the order of 0.01 to 10% by
weight based on the total amount (total mass) of the ink composition.

[0219]--Conductive Salt--

[0220]For the purpose of controlling discharge properties, the ink
composition of the invention, in particular, the ink composition for the
inkjet recording may contain a conductive salt such as potassium
thiocyanate, lithium nitrate, ammonium thiocyanate, or dimethylamine
hydrochloride.

[0221]--Solvent--

[0222]It is also effective to add a trace amount of organic solvent to the
ink composition of the invention in order to improve the adhesion to
between a recording medium and the formed image.

[0223]Examples of the solvent include ketone-based solvents such as
acetone, methyl ethyl ketone, and diethyl ketone, alcohol-based solvents
such as methanol, ethanol, 2-propanol, 1-propanol, 1-butanol, and
tert-butanol, chlorine-based solvents such as chloroform and methylene
chloride, aromatic-based solvents such as benzene and toluene,
ester-based solvents such as ethyl acetate, butyl acetate, and isopropyl
acetate, ether-based solvents such as diethyl ether, tetrahydrofuran, and
dioxane, and glycol ether-based solvents such as ethylene glycol
monomethyl ether and ethylene glycol dimethyl ether.

[0224]In this case, the solvent is effectively added in such a range that
deterioration in solvent resistance is not caused, and the amount of the
solvent is preferably in the range of 0.1 to 5% by weight, more
preferably 0.1 to 3% by weight, relative to the total amount of the ink
composition.

[0225]--Polymer Compound--

[0226]The ink composition of the invention may contain various types of
polymer compounds different in structure from (A) the specific polymer,
in order to adjust film physical properties. Examples of the polymer
compounds include acrylic polymers, polyvinylbutyral resins, polyurethane
resins, polyamide resins, polyester resins, epoxy resins, phenol resins,
polycarbonate resins, polyvinylbutyral resins, polyvinylformal resins,
shellac, vinylic resins, acrylic resins, rubber-based resins, waxes, and
other natural resins. They may be used in a combination of two or more
types. Among these, a vinylic copolymer obtained by copolymerization of
an acrylic monomer is preferable. As a copolymer component of the polymer
compound, a copolymer including a "carboxyl group-containing monomer", an
"alkyl methacrylate ester" or an "alkyl acrylate ester" as a structural
unit may preferably be used.

[0227]Besides, the ink composition of the invention may as necessary
contain, for example, a leveling additive, a matting agent, a wax for
adjusting film physical properties, or a tackifier in order to improve
the adhesion to a recording medium such as polyolefin or PET, the
tackifier not inhibiting polymerization.

[0228]Specific examples of the tackifier include high molecular weight
tacky polymers described on pp. 5-6 of JP-A No. 2001-49200 (e.g. a
copolymer formed from an ester of (meth)acrylic acid and an alcohol
having an alkyl group with 1 to 20 carbons, an ester of (meth)acrylic
acid and an alicyclic alcohol having 3 to 14 carbons, or an ester of
(meth)acrylic acid and an aromatic alcohol having 6 to 14 carbons), and a
low molecular weight tackifying resin having a polymerizable unsaturated
bond.

[0229]<Preferably Physical Properties of the Ink Composition>

[0230]The ink composition of the invention is cured with high sensitivity
to form images excellent in blocking resistance and is preferably applied
particularly to the inkjet recording method.

[0231]When the ink composition of the invention is applied to inkjet
recording, the ink viscosity at jetting temperature is preferably 5 to 30
mPas, more preferably 7 to 20 mPas, in consideration of jetting
properties. Accordingly, the composition ratio is appropriately regulated
and determined preferably such that the above range is reached.

[0232]The viscosity of the ink composition at room temperature (25 to
30° C.) is preferably 7 to 120 mPas, more preferably 10 to 80
mPas. By setting the viscosity at room temperature high even if a porous
recording medium is used, penetration of the ink into the recording
medium can be prevented, uncured monomers can be reduced and the odor can
be reduced. Furthermore, ink spreading when ink droplets have landed can
be suppressed, and as a result there is the advantage that the image
quality is improved.

[0233]The surface tension of the ink composition of the invention is
preferably 20 to 40 mN/m, more preferably 20 to 30 mN/m. When the ink
composition of the invention is recorded on various recording media such
as polyolefin, PET, coated paper and non-coated paper, the surface
tension thereof is preferably 20 mN/m or more for prevention of ink
bleeding and penetration and 30 mN/m or less for wetting properties.

[0234]The ink composition of the invention can be used preferably as an
inkjet recording ink. The inkjet recording system is not particularly
limited and may be any known method such as an electrostatic control
method which utilizes electrostatic attraction to jet ink, a
drop-on-demand method (pressure pulse method) utilizing vibrational
pressure of piezoelectric element, an acoustic ink jet method which
includes converting electrical signal to acoustic beam with which the ink
is irradiated to produce a radiation pressure that is utilized to jet the
ink, and a thermal ink jet method which includes heating the ink to form
bubbles that raise the pressure to jet the ink. The inkjet recording
systems include a system of jetting a lot of small volume droplets of a
so-called photo ink having a low concentration, a system of using
multiple inks that have substantially the same hue and a different
concentration for improving image quality, and a system of using a
transparent and colorless ink.

[0235]Among them, the ink composition of the invention is preferable as an
inkjet recording ink in a drop-on-demand system (pressure pulse system)
of using a piezoelectric element.

[0236]<Inkjet Recording Method>

[0237]The ink composition of the invention can be used in an inkjet
recording method including (a) jetting the ink composition onto a
recording medium (image recording step) and (b) curing the ink
composition by irradiating the jetted ink composition with active energy
rays (image curing step).

[0238]That is, the inkjet recording method of the invention is a method
including the image recording step and the image curing step, wherein an
image is formed by inkjet recording.

[0239]In the image curing step in the invention, active energy rays are
used in the image curing step, then a recording material is recorded with
an image in the image recording step, then the recorded image is
irradiated with active energy rays, thereby allowing the polymerizable
compound contributing to image formation to proceed thus forming an
excellently cured and highly rigid image.

[0240]In the image curing step, an exposure processing for promoting
polymerization curing can be conducted with a light source for emitting
an active energy ray in a wavelength region corresponding to the
responsive wavelength of the ink composition. The light source, exposure
time and light quantity may be selected appropriately depending on the
degree of the polymerization curing of the polymerizable compound in the
invention.

[0241]The thickness of the image cured in the image curing step is
preferably 2 to 30 μm. As used herein, "the thickness of the image"
refers to the thickness of a cured product of the image formed from the
ink composition. When the thickness of the image is 2 to 30 μm, the
image of from low to high density can be manifested.

[0242]In the image curing step, an exposure processing for promoting
polymerization curing can be carried out with a light source for emitting
an active energy ray in a wavelength range corresponding to the
responsive wavelength of the ink composition. Specifically, a light
source for emitting an active ray in the wavelength range of 250 to 450
nm, preferably 365±20 nm, for example, LD, LED (light emitting diode),
a fluorescent lamp, a low-pressure mercury lamp, a high-pressure mercury
lamp, a metal halide lamp, a carbon arc lamp, a xenon lamp, a chemical
lamp or the like may be preferably used in curing. Preferable light
sources include LED, a high-pressure mercury lamp, a metal halide lamp,
and the like.

[0243]When curing with radical polymerization, the polymerization is
inhibited with oxygen and can thus be carried out with curing in a state
of low oxygen concentration, that is, curing the low energy by exposing
in a gas atmosphere with nitrogen or the like.

[0244]One characteristics of the ink composition of the invention is that
the function of (A) the specific polymer can suppress the polymerization
inhibition with oxygen thereby attaining excellent curability without
requiring the curing step in an inert gas atmosphere.

[0245]Prints obtained using this ink have an image area that has been
cured by exposure to radiations such as ultraviolet rays to make the
image area excellent in strength, and thus the product of the invention
can be used as an ink receiving layer (image area) of a surface printing
plate.

[0246]In the recording step, an inkjet recording method using an inkjet
printer is preferably used. Specifically, the image recording step is
conducted preferably by recording the image with the ink composition to
be jetted by inkjet recording.

[0247]In the inkjet recording method, the ink composition is jetted
preferably after the ink composition is heated to 40 to 80° C. and
the viscosity of the ink composition is lowered to 30 mPas or less,
preferably 20 mPas or less, and by using this method, high jetting
stability can be realized. Commonly, radiation-curing ink compositions
have higher viscosity than that of aqueous inks and are thus liable to a
significant viscosity fluctuation range resulting from temperature
fluctuation during printing. The viscosity fluctuation of the ink
composition has great influences on the change of droplet size and
droplet jetting speed, thus consequently leading to deterioration in
image quality and thus the temperature of the ink composition during
printing should be made as constant as possible. For this purpose, the
recording method preferably has an ink temperature detection unit, an ink
heating unit, and a regulating unit for regulating heating in accordance
with the temperature of the ink detected.

[0248]The method of controlling the temperature is not particularly
restricted. For instance, a temperature sensor is preferably disposed to
each of plural piping sites to apply heating control corresponding to the
flow rate of the ink composition and the environmental temperature. The
heating head unit is preferably thermally shielded or insulated so as to
minimize the environmental influence such as outdoor air against the unit
itself. It is preferable to insulate the head unit from other units and
reduce the heat capacity of the entire heating unit in order to shorten
the start-up time needed for heating or in order to reduce the loss of
heat energy. Alternatively, a unit for regulating applied energy to jet
the ink in accordance with the temperature of the ink is also preferable.

[0249]The control range for the temperature of the ink composition is
preferably ±5° C. relative to a set temperature, preferably
±2° C. relative to the set temperature, more preferably
±1° C. to the set temperature.

[0250]The amount of ink droplets landed onto a recording medium is
preferably capable of being regulated in an arbitrary amount between 0.05
to 25 g/m2 in order to realize excellent tone. For this realization,
the size and numbers of ink droplets jetted from a head are preferably
regulated.

[0251]When the distance between a head and a recording material is too
long, the landing of ink droplets is disturbed by the movement of air
accompanying the head or the recording material, thereby lowering the
positional accuracy of landing. On the other hand, when the distance is
too short, the head and the recording material may be contacted with each
other due to the uneven surface of the recording material and vibration
attributable to a delivery mechanism and thus the distance therebetween
is preferably kept at about 0.5 to 2 mm.

[0252]Ink Set

[0253]The ink may be in one color, in cyan, magenta and yellow colors, in
4 colors that are these colors plus black, or in those colors further
containing other specific colors. The colorant may be a dye or pigment.
The order of jetting these inks may be such that the inks are landed with
increasing brightness or with decreasing brightness, and the inks are
landed preferably in a preferable order of image recording qualities.

[0254]When ink is superposed starting from one that is highest in the
brightness, active energy rays comes easy to reach lower ink, thus making
it possible to expect inhibition of curing sensitivity, reduction of
residual monomers, reduction of odor, and an improvement in adhesiveness.
The irradiation can be performed in block after all colors are
discharged. However, exposure for every color is preferable from the
viewpoint of promotion of the curing.

[0255]Image signals to be recorded are preferably subjected to signal
processing to attain excellent color reproduction as described in, for
example, JP-A No. 6-210905.

[0256]The use aspect of the ink composition of the invention is not
limited to the inkjet recording method described above. The ink
composition of the invention can be applied for example to the formation
of an image wherein in the image recording step, an ink image is formed
on a recording medium by a method other than inkjet recording and then
irradiated with an active energy ray in the image curing step, or to the
formation of an image wherein the ink composition is jetted with an
inkjet recording unit, onto a recording material and then the image is
cured.

[0257]The ink composition of the invention can be used not only to inkjet
recording applications but also to three-dimensional modeling
applications, for example, applications to formation of a printing
ink-receiving part of the surface printing plate, as well as applications
to can printing and foods. Among these applications, known methods can be
utilized to form an image with reference to, for example, Japanese Patent
No. 2979586 or the like.

[0258][Recording Medium]

[0259]Both an ink-penetrable recording medium and a non-ink-penetrable
recording medium can be used as recording mediums used with the ink
composition of the invention. Examples of the ink-penetrable recording
media include plain paper, inkjet-exclusive paper, coated paper,
electrophotographic common-use paper, cloth, nonwoven fabric, porous
film, polymer absorbent, and the like. These recording media are
described as the "recording materials" in JP-A No. 2001-1891549 and
others.

[0260]Examples of the non-ink-penetrable recording media include art
paper, synthetic resin, rubber, resin-coated paper, glass, metal,
ceramics, wood, and the like. In addition, a composite material in
combination with these materials may also be used for expression of other
functions.

[0261]Any synthetic resins may be used as the synthetic resin, and
examples thereof include polyesters such as polyethylene terephthalate
and polybutadiene terephthalate, polyolefins such as polyvinyl chloride,
polystyrene, polyethylene, polyurethane and polypropylene, acrylic
resins, polycarbonate, acrylonitrile-butadiene-styrene copolymers,
diacetate, triacetate, polyimide, cellophane, celluloid, and the like.

[0262]The shape (thickness) of a substrate using the synthetic resin may
be in the shape of film, card, or block and can be suitably selected for
desired purposes without particular limitation. The synthetic resin may
be transparent or opaque. The synthetic resin is preferably used as in
the shape of so-called soft packaging film, and various non-absorptive
plastics and the films thereof may be used. Examples of the various
plastic films include polyethylene terephthalate (PET) film, biaxially
orientated polystyrene (OPS) film, biaxially orientated polypropylene
(OPP) film, biaxially orientated nylon (ONy) film, polyvinyl chloride
(PVC) film, polyethylene (PE) film and triacetyl cellulose (TAC) film.

[0263]Examples of the resin-coated papers include transparent polyester
film, opaque polyester film, opaque polyolefin resin film, paper supports
laminated with a polyolefin resin on both faces and particularly
preferable are the paper supports laminated with a polyolefin resin on
both faces.

[0264]As described above, image recording using the ink composition of the
invention can be used to give images which are cured with high
sensitivity, are free from surface tackiness and are free of change in
tack with time, so that the resulting print has an image excellent in
blocking resistance, and the prints even when stored and delivered in a
laminated state are free of deterioration in workability attributable to
adhesion of an image region to its adhesive non-image medium.

[0265]Exemplary aspects of the invention are enumerated as below:

[0266]<1> An ink composition comprising:

[0267](A) a polymer compound having (a-1) a photoradical generation site
and (a-2) at least one segregation site selected from a fluoroalkyl
group, a siloxane structure, and a long-chain alkyl group;

[0268](B) a radical-polymerizable compound, and

[0269](C) a photoradical generator having a structure different from that
of (A).

[0270]<2> The ink composition of <1>, wherein the polymer
compound (A) comprises, as a structural unit containing a photoradical
generation site (a-1), at least one structural unit represented by any of
formulae (a-1-1) to (a-1-7), or at least one structural unit represented
by formulae (a-1-8) or (a-1-9):

##STR00045##

[0271]wherein R10 represents a hydrogen atom or a methyl group; L
represents a single bond or a divalent linking group; R11, R12,
R13 and R14 each independently represent a linear, branched or
cyclic hydrocarbon group having 1 to 12 carbon atoms which may have a
substituent; R11 and R12, and R13 and R14 may be
bound to form a cyclic structure having a cycle consisting of 8 or less
carbon atoms;

[0272]R15 and R16 each independently represent a linear,
branched or cyclic hydrocarbon group having 1 to 12 carbon atoms which
may have a substituent;

[0273]R17 represents a hydrogen atom or a linear or branched alkyl
group having 1 to 6 carbon atoms; and R18, R19, and R20
each independently represent a hydrogen atom or a hydrocarbon group
having 1 to 12 carbon atoms;

##STR00046##

[0274]wherein R21, R22, R23, R24 and R25 each
independently represent a hydrogen atom, a linear, branched or cyclic
alkyl group having 1 to 8 carbon atoms, a phenyl group, a hydroxyl group,
or an alkyl group-substituted amine group, and two of R21, R22,
and R23 to R25 may be bound to each other to form a ring
structure; R26 and R27 each represent a hydrogen atom, an alkyl
group having 1 to 6 carbon atoms, or a halogen atom;

[0275]R28, R29, R30 and R31 each independently
represent a hydrogen atom, a linear or branched alkyl group having 1 to 6
carbon atoms, a halogen atom, or a hydroxyl group; and

[0276]R10 and L have the same meanings as defined in the formula
(a-1-1);

##STR00047##

[0277]wherein R32, R33, R34 and R35 each independently
represent a hydrogen atom, a hydroxyl group, a halogen atom, or a linear
or branched alkyl, alkenyl or alkynyl group having 1 to 20 carbon atoms,
and the alkyl group may, in its alkyl chain, have non-consecutive oxygen
atoms; and

[0278]L has the same meaning as defined in the formula (a-1-1).

[0279]<3> The ink composition of <1> or <2>, wherein a
weight-average molecular weight of (A) the polymer compound is from 5000
to 100,000.

[0280]<4> The ink composition of any one of <1> to <3>,
wherein (A) the polymer compound further includes (a-3) a radical
polymerization site.

[0281]<5> The ink composition of any one of <1> to <4>,
wherein a glass transition temperature (Tg) of (A) the polymer compound
determined by differential scanning calorimetry (DSC) is 20 to 80°
C.

[0282]<6> A method for inkjet recording, the method comprising:

[0283](i) jetting the ink composition according to any one of <1> to
<5> onto a recording medium, and

[0284](ii) irradiating the jetted ink composition with an active energy
ray, to cure the ink composition.

EXAMPLES

[0285]Hereinafter, the present invention will be described with reference
to the Examples, but the invention is not limited thereto.

Synthesis Example 1

1. Synthesis of Synthetic Monomer 1

[0286]A 500-mL three-neck flask was charged with 263 g of chloroform, 50.1
g of phenoxyethyl acrylate and 36.7 g of benzoyl chloride, and the
mixture was stirred on an ice bath at 0° C., while 34.7 g of
aluminum chloride was added thereto, and the mixture was reacted at room
temperature for 8 hours. The reaction mixture was washed with sodium
bicarbonate water and then with water, dried over calcium chloride and
fractionated through a column into the object product to give a synthetic
monomer 1 with 66% yield having the structure shown below.

2. Synthesis of Synthetic Monomer 2

[0287]A synthetic monomer 2 having the structure shown below was obtained
with 60% yield in the same manner as in synthesis of the synthetic
monomer 1 except that 4-cyanobenzoyl chloride was used in place of
benzoyl chloride, and the reaction was carried out for 24 hours.

3. Synthesis of Synthetic Monomer 3

[0288]A synthetic monomer 3 was obtained with 62% yield in the same manner
as in synthesis of the synthetic monomer 1 except that 4-methylbenzoyl
chloride was used in place of benzoyl chloride, and the reaction was
carried out for 12 hours.

4. Synthesis of Synthetic Monomer 4

[0289]A synthetic monomer 4 was obtained with 64% yield in the same manner
as in synthesis of the synthetic monomer 1 except that 4-methoxybenzoyl
chloride was used in place of benzoyl chloride, and the reaction was
carried out for 12 hours.

##STR00048##

5. Synthesis of Synthetic Monomer 5

[0290]A synthetic monomer 5 having the structure shown below was obtained
with 90% yield in the same manner as described in Macromol. Chem. Phys.
2006, 207, 1080-1086.

6. Synthesis of Synthetic Monomer 6

[0291]60 g of hydroxyethyl benzene thiol and 44.7 g of chloride acrylate
were reacted in 244 g of pyridine at 25° C. for 4 hours and then
formed by distillation into 2-(phenylthio)ethyl acrylate with 80% yield.
A synthetic monomer 6 was obtained with 82% yield in the same manner as
in Synthesis Example 1 except that 2-(phenylthio)ethyl acrylate was used
in place of phenoxyethyl acrylate.

7. Synthesis of Synthetic Monomer 7

[0292]A synthetic monomer 7 was obtained with 65% yield in the same manner
as in synthesis of the synthetic monomer 1 except that 4-phenylbenzoyl
chloride was used in place of benzoyl chloride, and the reaction was
carried out for 12 hours.

##STR00049##

8. Synthesis of Synthetic Monomer 8

[0293]2.42 g of Compound B having the structure below and 0.10 g of DMAP
(dimethyl amiopyridine) were dissolved in 20 mL THF and then 2.32 g of
Compound C having the structure below was added. Then, the mixture was
cooled to 0° C. on a cooling bath, and DCC (dicyclohexyl
carbodiimide) was added gradually. Then, the temperature of the mixture
was increased to room temperature followed by stirring for 3 hours. After
the reaction was finished, water was added to the reaction solution which
was then extracted with ethyl acetate. The extract was washed with dilute
hydrochloric acid. then washed with saturated saline, dried over
magnesium sulfate and filtered, and the filtrate was concentrated with an
evaporator. The concentrated filtrate was purified with a silica gel
column to give a synthetic monomer 8 with a yield of 2.8 g having the
structure below. The compound B can be synthesized by a method described
in JP-A No. 2-255677.

##STR00050##

9. Synthesis of Synthetic Monomer 9

[0294]2.08 g of Compound A having the structure below was dissolved in 10
mL of 2-butanone and then added to 1.11 g of triethylamine. Further, the
mixture was cooled to 0° C. on a cooling bath, and 1.00 g of
acrylic acid chloride was added gradually. Thereafter, the temperature of
the mixture was increased to room temperature followed by stirring for 3
hours. After the reaction was finished, water was added to the reaction
solution which was then extracted with ethyl acetate. The extract was
washed with saturated saline, then dried over magnesium sulfate and
filtered, and the filtrate was concentrated with an evaporator. The
concentrated filtrate was purified with a silica gel column to give a
synthetic monomer 9 with a yield of 1.8 g having the structure below.

##STR00051##

10. Synthesis of Synthetic Monomer 10

[0295]A synthetic monomer 10 having the structure shown below was
synthesized according to a method described in Macromol. Chem. Phys.
2002, 203, pp. 1486-1496.

##STR00052##

11. Synthesis of Synthetic Monomer 11

[0296]A small amount of NEOSTANE U600 was added to 10 g of KARENZ MOI
(manufactured by Showa Denko K.K.) and 43.8 g of one-terminal hydroxyl
group-modified silicone (manufactured by Chisso Corp.) in a 500-mL
three-neck flask, and the mixture was reacted at 60° C. for 10
hours. The reaction mixture was recrystallized from IPA to give 53 g of
Synthetic Monomer 11.

12. Synthesis of Synthetic Monomer 12

[0297]A synthetic monomer 12 having the structure shown below was obtained
with 38% yield according to a method described in Polymer, 45, (2004),
5057-5063.

##STR00053##

13. Synthesis of Synthetic Monomers 13 and 14

[0298]Synthetic Monomers 13 and 14 were synthesized according to a method
described in "Journal of Heterocyclic Chemistry" (1990), 7(5), P. 1241-4
and obtained with 40% and 36% yields respectively.

##STR00054##

14. Synthesis of Synthetic Monomers 15 to 16

[0299]Synthetic Monomers 15 and 16 were synthesized according to a method
described in Macromol. Rapid Commun. (2004), 25, pp. 748-752 and obtained
with 55% and 62% yields respectively.

##STR00055##

Synthesis Example 2

(A) Synthesis of Specific Polymer (a-1)

[0300]A 500-mL three-neck flask was charged with 68.2 g of a solvent
methyl ethyl ketone (MEK), 20 g of a polymerizable compound styrene, 9.2
g of R-1620 (trade name, manufactured by Daikin Industries, Co.), and
0.066 g of a polymerization initiator V-65 (manufactured by Wako Pure
Chemical Industries, Ltd.), and the mixture was reacted at 70° C.
for 12 hours. Thereafter, 34.8 g of chloride 2-acetoxyisobutyrate, 21.4 g
of triethylamine, and 28.2 g of aluminum chloride were added thereto at
0° C., then returned at room temperature (25° C.) and
reacted at 24 hours. The reaction mixture was poured into a large amount
of water, the resulting residues were dissolved in 50 g of THF, 10 g of
methanol and 5 g of LiOH were added thereto, and the mixture was reacted
at room temperature for 24 hours. The reaction mixture was dissolved in
tetrahydrofuran (THF) and then poured onto a large amount of water
thereby being re-precipitated; this re-precipitation purification was
repeated 3 times. The specific polymer (a-1) was thus obtained.

Synthesis Example 3

(A) Synthesis of Specific Polymers (a-2) to (a-4)

[0301]Specific polymers (a-2) to (a-4) were obtained in the same manner as
in synthesis of the specific polymer (a-1) except that the monomers in
Table 1 below were added in place of the monomer R-1620 used in the
Synthesis Example 2.

Synthesis Example 4

(A) Synthesis of Specific Polymers (a-5) to (a-15) and (a-17)

[0302]The monomer shown in the table and 30 wt % MEK were added to a
500-mL three-neck flask, and then V-65 (manufactured by Wako Pure
Chemical Industries, Ltd.) was added in an amount of 0.15 mole and
reacted at 70° C. for 12 hours. The mixture was dissolved in THF
and poured into a large amount of hexane; this re-precipitation
purification was repeated 3 times. Specific polymers (a-5) to (a-15) and
(a-17) were thus obtained with yield of from 90% to 98%.

Synthesis Example 5

(A) Synthesis of Specific Polymer (a-16)

[0303]A 500-mL three-neck flask was charged with 30 g of toluene, 15 g of
the synthesis monomer 10 shown in the table, 5.93 g of the synthetic
monomer 11, and 0.024 g of V-65 (manufactured by Wako Pure Chemical
Industries, Ltd.), and the mixture was reacted at 70° C. for 12
hours. Thereafter, the mixture was subjected to polymer reaction based on
a description of Macromol. Chem. Phys. 2002, 203, 1486, and then poured
into a large amount of hexane and filtered to give the specific polymer
(a-16) with 64% yield.

Synthesis Example 6

(A) Synthesis of Specific Polymers (a-18) to (a-23)

[0304]A 500-mL three-neck flask was charged with the monomer shown in the
table, 40 wt % MEK, 500 ppm of NEOSTANE U600 (manufactured by Nitto Kasei
Co., Ltd.) and 750 ppm of TEMPO, and the mixture was reacted at
60° C. for 12 hours. A small amount of methanol was added to the
mixture which was then reacted for 2 hours and poured into a large amount
of hexane for re-precipitation purification. After filtration and drying,
specific polymers a-18 and a-23 were obtained.

Synthesis Example 7

7-1. Synthesis of Comparative Compound 1

[0305]A 500-mL three-neck flask was charged with 68.2 g of a solvent
methyl ethyl ketone (MEK), 20 g of a polymerizable compound styrene, 9.2
g of R-1620 (trade name, manufactured by Daikin Industries, Co.), and
0.066 g of a polymerization initiator V-65 (manufactured by Wako Pure
Chemical Industries, Ltd.), followed by reaction at 70° C. for 12
hours, thereby giving 29 g of Comparative Compound 1 that is a copolymer
compound having the same fluorine-based segregation surface site as in
the specific polymer (a-1).

7-2. Comparative Compound 2

[0306]Comparative Example 2 is ESACURE KIP150 (polymer initiator having
the following structural unit) manufactured by DAICEL UCB. This
commercial product was re-precipitated with hexane, dried and used as
solids.

##STR00056##

7-3. Comparative Compound 3

[0307]The following comparative compound 3, that is, a
low-molecular-weight initiator having a surface segregation surface site,
was synthesized by a method described in Japanese Patent Application
National Publication (Laid-Open) No. 2004-506639.

[0309]Ink compositions were prepared in the same manner as in Example 1
except that the polymers shown in Tables 3 and 4 were used in place of
(A) the specific polymer used in the example 1, and the same evaluation
was conducted as in Example 1.

Comparative Examples 1 to 4

[0310]Ink compositions were prepared in the same manner as in Example 1
except that Comparative Compounds 1 to 3 obtained in Synthesis Example 7
shown in Table 4 were used in place of (A) the specific polymer used in
the example 1 or without using any specific polymer or comparative
compounds, and the same evaluation was conducted as in Example 1.

[0313]The yellow ink composition thus produced was printed on a polyvinyl
chloride sheet, then passed at the predetermined rate under rays of an
ultraviolet-emitting diode (UV-LED) and irradiated by regulation of
specified light exposure. Prints with this ink were evaluated under the
following criteria, and the results are shown in Tables 3 and 4 below.

[0314]<Inkjet Image Recording>

[0315]First, the prepared ink composition was filtered with a filter
having an absolute filtration accuracy of 2 μm.

[0316]Then, a commercial inkjet recording device having a piezo system
inkjet nozzle was used in recording a recording medium. The ink supply
system includes a main tank, a supply pipe, an ink supply tank
immediately before an inkjet head, a filter, and a piezo system inkjet
head, and a section from the ink supply tank to the inkjet head was
thermally insulated and heated. Temperature sensors were provided on the
ink supply tank and in the vicinity of the nozzle of the inkjet head, and
the temperature was controlled so that the nozzle section was always at
70° C.±2° C. The piezo system inkjet head was driven so
as to discharge a multisize dot of 8 to 30 μL at a resolution of
720×720 dpi. The "dpi" as used herein means the number of dots per
2.54 cm.

[0317]Using the inkjet recording device, the ink composition after
filtration was jetted at ambient temperature (25° C.) and
irradiated by means of UV-LED, NCCUO33 manufactured by Nichia
Corporation. The LED emits UV light at a wavelength of 365 nm from 1
chip, and by applying a current of about 500 mA, light of about 100 mW is
emitted from the chip. Plural thereof were aligned at intervals of 7 mm
to give a power of 0.3 W/cm2 on the surface of a recording medium.
The time from landing to exposure, and the exposure time, can be varied
by the transport speed of the medium and the distance between a head and
the LED in the transport direction. In this example, irradiation was
carried out about 0.2 sec. after landing.

[0318]The exposure energy on the recording medium can be regulated between
0.01 to 15 J/cm2, depending on the settings of the distance between
the UV-LED and the recording medium and of the transport speed of the
recording medium. The irradiation was continued until the feeling of
tackiness disappeared on the image surface after irradiation with
ultraviolet rays. As the recording medium, a flexible polyvinyl chloride
sheet was used.

[0319](Evaluation of Jetting Stability)

[0320]The ink composition (after filtration) obtained as described above
was evaluated for its jetting stability through head nozzles in the
following manner.

[0321]That is, the number of nozzles lost in continuous jetting for 60
minutes was measured with a commercial inkjet recording device having
piezo system inkjet nozzles, under the following conditions.

[0327]In this experiment, the ink composition was jetted onto a PET
substrate and then exposed to rays (exposure: 1,000 mW/cm2), upon
which lost nozzles (clogged nozzles) were counted.

[0328]--Evaluation Criteria--

[0329]A: The number of lost nozzles is 0 or more to less than 5.

[0330]B: The number of lost nozzles is 5 or more to less than 10.

[0331]C: The number of lost nozzles is 10 or more.

[0332](Evaluation of Transfer Sensitivity)

[0333]The exposure energy intensity (mJ/cm2) when the feeling of
tackiness disappeared on the image surface after irradiation with
ultraviolet rays was defined as transfer sensitivity.

[0334]The smaller the value, the higher the sensitivity.

[0335]The allowable range of transfer sensitivity in this evaluation
method is 2000 mJ/cm2 or less, more preferably 1500 mJ/cm2 or
less.

[0336](Evaluation of Abrasion Resistance)

[0337]A sample having a solid image printed at a resolution of
720×720 dpi on a flexible polyvinyl chloride sheet was rubbed with
an eraser (trade name: K-50 PLASTIC ERASER KEEP, manufactured by
Hoshiya), and its transfer onto the eraser was evaluated. The evaluation
criteria are as follows:

[0338]--Evaluation Criteria--

[0339]A: There is no transfer.

[0340]C: There is transfer.

[0341](Evaluation of Blocking Sensitivity)

[0342]On an image after irradiation with UV rays obtained by applying the
inkjet recording method were stuck 500 sheets of PET (size: the same size
as the flexible polyvinyl chloride having an image formed both in length
and breadth, weight: 2 g/sheet), and then the PET was left for 1 day and
evaluated visually for its transfer. A was given when there was no
transfer, while C was given when there was transfer, and the exposure
energy intensity (mJ/cm2) required for disappearance of transfer was
defined as blocking sensitivity.

[0345]A cured film was prepared in the same manner as in the evaluation of
exposure sensitivity except that the integrated exposure intensity was
12,000 mJ/cm2, the illumination intensity was 2140 mW/cm2, and
FASSON PE (polyethylene film (film thickness: 100 μm) manufactured by
Fasson) was used as a support in place of the flexible polyvinyl
chloride. The resulting cured film was cut in sizes of 5 cm (shaft
length)×2.5 cm (width) and stretched at a speed of 30 cm/min with a
tensile strength machine (trade name: AUTOGRAPH AGS-J, manufactured by
Shimadzu Corporation) to determine the degree of stretching at which the
cured film was ruptured. The state stretched from the initial length to
the twofold length was defined as 100%.

[0346]The allowable range of stretching ratio is 200% or more, more
preferably 300% or more.

[0349]The cyan ink composition thus produced was printed on a polyvinyl
chloride sheet, then passed at the predetermined rate under rays of an
ultraviolet-emitting diode (UV-LED) and irradiated by regulation of
specified light exposure. Prints with this ink were evaluated in the same
manner as in Example 1. The results are shown in Tables 3 and 4 below.

[0352]The black ink composition thus produced was printed on a polyvinyl
chloride sheet, then passed at the predetermined rate under rays of an
ultraviolet-emitting diode (UV-LED) and irradiated by regulation of
specified light exposure. Prints with this ink were evaluated in the same
manner as in Example 1. The results are shown in Tables 3 and 4 below.

[0354]From the results in Tables 3 and 4, it can be seen that the ink
compositions in the Examples, containing (A) the specific polymer in the
invention, are cured with high sensitivity, and the resulting ink images
significantly improve tack sensitivity and blocking sensitivity while
maintaining flexibility.

[0355]It can been seen that even when the composition has a segregation
site but has no photoradical polymerization site as shown in Comparative
Example 2, and even when the composition has both of them but has a
low-molecular-weight compound as shown in Comparative Example 3, their
addition does not bring about the effect of the invention.

[0356]According to the invention, there can be provided an ink composition
preferable for use in inkjet recording, which is curable with high
sensitivity, with active energy rays, and can form images excellent in
abrasion resistance and blocking resistance.

[0357]The ink composition of the invention can be used to provide an
inkjet recording method capable of forming images excellent in blocking
resistance on a recording material.